This invention relates to an offset printing press comprising a mechanism for moving at least one roller in a water supply portion close to and away from another roller therein.
In general, there is a well-known offset printing press in which water and ink are supplied to a printing plate attached onto the outer surface of a plate cylinder, and then they are transferred to a blanket cylinder, while printing sheets are fed between the blanket cylinder and an impression cylinder for printing.
The above offset printing press comprises a water supply portion and an ink supply portion, and the water supply portion comprises a forme dampening roller contacting the printing plate onto the plate cylinder, a water fountain roller immersed into water in a water pan, and intermediate roller means intervening between the water fountain roller and the forme dampening roller for transferring the water therebetween. The intermediate roller means comprises a water oscillating roller capable of reciprocating in its axial direction with contacting the forme dampening roller for leveling a thickness of water thereon. Such an offset printing press is disclosed, for example, in Japanese Patent Laid-Open Publication HEI1(1989)-280556.
In the above offset-printing press, if each of the water oscillating roller and the forme dampening roller has a hydrophilic property on each outer surface, it is no problem to contact these two rollers with each other at all times. However, if the water oscillating roller has a hydrophilic property on its outer surface, while the forme dampening roller has a lipophilic property on its outer surface, some troubles may be occurred while supplying water. For example, in case that the offset printing press is re-driven after a printing operation is once finished, water does not attach to the water oscillating roller, and thereby it is difficult to supply the water to the plate cylinder stably, since the ink on the forme dampening roller is transferred onto the water oscillating roller before the water is supplied thereon. Therefore, an operator of the offset printing press must wipe off the ink from the water oscillating roller before re-driven the offset printing press, and this work makes the printing operation troublesome.